This invention relates to a device and a method for inserting or embedding, into a digital image, an electronic watermark which may identify a copy right and the like.
Recently, popularization of digital satellite broadcast, internet, a DVD (digital video disc) makes it possible to easily get digital images by users. Since such digital images are not degraded in image quality even by being repeatedly copied, protection of a copy right becomes very important more and more. In order to ensure copy right protection, proposals have been made about a technique of embedding information related to a copy right and the like into DCT (discrete cosine transform) coefficients obtained from digital images.
Specifically, a conventional technique uses an electronic watermark insertion circuit that is operable in response to a sequence of digital images subjected to preprocessing. In such an electronic watermark insertion circuit, an electronic watermark is inserted or embedded into the preprocessed digital images at an invariable watermark strength once insertion of such an electronic watermark is started. In other words, the watermark strength can not be changed until insertion of the electronic watermark is stopped.
With this conventional technique, such an electronic watermark should be inserted at a weak watermark strength even when the digital images are weak in a detection ability of detecting the inserted watermark. This makes it difficult to detect the inserted electronic watermark. To the contrary, the electronic watermark is inserted at a strong watermark strength when the digital images are strong in the detection ability, which inevitably results in deterioration of the image quality.